Human Lyme borreliosis (LB), commonly known as Lyme disease, is the most prevalent vector-borne infection in temperate climate zones around the world. Lyme disease is caused by bacterial spirochetes belonging to the genus Borrelia, and three pathogenic species of Borrelia, in particular, are associated with Lyme disease in humans: Borrelia burgdorferi, Borrelia garinii, and Borrelia afzelii. Borrelia burgdorferi causes of Lyme disease in North America, whereas Borrelia garinii and Borrelia afzelii are the causative agents in most European and Asian cases. Borrelia is mainly transmitted to humans by the bite of infected ticks belonging to a few species of the genus Ixodes, such as the blacklegged tick (or deer tick, Ixodes scapularis) that spreads the disease in the northeastern, mid-Atlantic, and north-central United States, and the western blacklegged tick (Ixodes pacificus) that spreads the disease on the Pacific Coast.
Lyme disease in humans is associated with inflammation and characterized by the skin lesion erythema migrans, as well as the potential development of neurologic, cardiac, and joint abnormalities. The Centers for Disease Control and Prevention now estimates based on preliminary statistics that the number of people newly diagnosed with Lyme disease each year in the United States alone is around 300,000. This is about ten times higher than the officially reported number of cases in the U.S., indicating that the disease is being vastly underreported. In Europe, approximately 85,000 Lynne disease cases occur annually.
The continued and marked prevalence of Lyme disease in the United States and throughout the world underscores the need for the development of an effective vaccine for the disease. Although clinical trials in the United States showed that Lyme disease could be prevented by vaccination with outer surface protein A (OspA), a major surface antigen encoded by all three Borrelia species associated with Lyme disease, the efficacy of the vaccine was limited to Borrelia burgdorferi due to antigenic heterogeneity of OspA across the three pathogenic Borrelia species. Currently, there exists no vaccine available in the United States for human Lyme disease caused by Borrelia burgdorferi, much less a vaccine that also protects against Borrelia garinii and/or Borrelia afzelii. Accordingly, there remains an unmet need in the field for the development of an effective Lyme disease vaccine, particularly a vaccine that would protect against Lyme disease caused by all three pathogenic Borrelia species.